Do you have a link to your test result? It should provide a list of assets that were not served from a CDN that it thought should be. Also, what is your user base? If you have users from around the world then it makes a lot of sense but if your users are all from one region then it may not be necessary.

Looking at your current results it looks like all of your static content is served from the main domain. If you want to use a CDN you can either sign up for one that lets you run your main HTML through it (like Cloudflare) or move all of your images, js and css to a static domain that is on a CDN.

If your user base is all local to the UK you probably don't want a CDN though so just make sure it actually makes sense. They will make it faster for a global audience but things might actually get slower for visits from the UK.